Thermal oil stimulation process



United States Patent O 3,490,531 THERMAL OIL STIMULATION PROCESS Henry 0. Dixon, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed May 27, 1968, Ser. No. 732,030 Int. Cl. E2lb 43/24 US. Cl. 166-260 8 Claims ABSTRACT OF THE DISCLOSURE An oil stratum around a well is opened up to increase oil flow and oil is produced therefrom by driving a combustion zone from adjacent the well radially into the stratum, followed by injection of cool liquid hydrocarbon, with or without suitable surfacants, into the heated stratum to cool and sometimes fracture the same, which may be followed by injecion of inert gas, sequentially, and thereafter opening up the well to flow of fluids, including oil. The liquid hydrocarbon may contain from 0.01 to weight percent of an oil-soluble surfactant stable at 650 F.

This invention relates to a process for producing oil from an oil stratum penetrated by a well and opening up the stratum around the well to improve flow of oil at temperatures which are not deleterious to the downhole equipment, including casing and tubing. It is an improvement over a similar process set forth in the copending US. patent application Ser. No. 671,980, filed Oct. 2, 1967, by F. A. Klein in that cool liquid hydrocarbon is used as the quenching and/or fracturing liquid instead of the water used by Klein. The cool liquid hydrocarbon has the advantages over water of not forming emulsions and of keeping the stratum oil wet.

The exposure of casing and tubing in production wells to temperatures in the range of 400 to 550 F. and higher has resulted in cracking, parting, and other detrimental elfects on the steel casing as well as cement damage. This condition has been encountered in the so-called huff-puff steam injection technique, causing shutdown and the need for removing and replacing the casing. Under such conditions, the increases in production costs are obvious. In a huff-puff fire flood operation, the in situ burning produces temperatures of the order of 1000 F. Such a process is disclosed in the copending application of I. C. Trantham, Ser. No. 408,157, filed Nov. 2, 1964, now US. Patent No. 3,332,482. It has been found that the produced oil flowing into the injection and production well following the burning phase of the operation raises the temperature of the casing and tubing to substantially higher temperatures than 400 F., is detrimental to the casing and tubing, and results in severe coking.

This invention is concerned with an improved method of operation, using in situ combustion and flow back into the injection well which avoids overheating the casing and down hole equipment and minimizes coking.

Accordingly, it is an object of the invention to provide an improved huff-pull in situ combustion or fire flood process for producing oil and/ or opening up the stratum around a production well in a reservoir under substantial original pressure. Another object is to provide a process for producing oil from an oil stratum by in situ huffpuif which avoids overheating of the downhole casing and tubing and minimize coking of oil in the stratum.

Patented Jan. 20, 1970 Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises initiating in situ combustion in an oil stratum around a well therein, driving the resulting combustion zone radially away from the well a substantial distance, such as 5 to 30 feet, preferably 10 to 25 feet, by air injection, thereafter terminating air injection, injecting a substantial slug of a cool liquid hydrocarbon through the well into the burned out zone so as to eflect partial cooling thereof and, if desired, thereafter injecting behind the cool liquid hydrocarbon a substantial slug of a cool inert gas, such as flue gas, and thereafter opening the Well to flow so that the pressure within the stratum produces the more fluid oil resulting from the heating operation. Permeability of the stratum around the well is substantially increased due to complete burnout of carbonaceous material and to fracturing induced by the high temperatures (900 F.+). By injecting a substantial slug of cool liquid hydrocarbon into the hot stratum in the burned out zone, this zone is cooled substantially and resulting hydrocarbon vapor is forced deeper into the stratum from the well, this hot zone being, if desired, further extended by the injection of cool combustion or flue gas which also adds to the cooling effect of the operation and reduces hydrocarbon saturation around the wellbore. Sufficient hydrocarbon and cooling gas are injected to reduce the temperature of the backflowing fluids, including oil, to not substantially more than 400 F.

The cool liquid hydrocarbon may be any hydrocarbon available having a carbon chain length of C (propane) to C (diesel fuel), or mixtures thereof. By cool is meant that no effort has been made to heat or cool it from its atmospheric temperature, although of course it will heat up some as it is pumped down the well into the hot burned out zone in the stratum. Diesel fuel, kerosene, or gasoline is preferred, C to C but any low carbon hydrocarbon can be used. Preferably this hydrocarbon should volatilize completely on the hot rocks, leaving very little residue on the rocks. These low carbon C to C hydrocarbons have the advantage of keeping the formation oil wet while producing no harmful emulsions.

In addition to reducing temperatures to a level relatively safe for producing equipment and less conducive to coking in the burned out zone, the injected fluids provide a number of additional benefits. Heat displaced into the unburned reservoir lowers the viscosity of the reservoir oil, thereby facilitating its flow to the production well. Carbon dioxide present in the injected gas and formed in the burning operation is dissolved in the reservoir oil, further reducing this viscosity as well as inducing swelling of the oil. Nitrogen present in the gas from both the injected air and the injected combustion gas is not absorbed but fills available pore space farther back in the reservoir, thereby providing additional expulsive energy for the reduced viscosity oil closer to the production well when backflow is initiated.

Special surfactants may be added to the injected hydrocarbons to increase their oil wetting characteristics. It is prefered to use from 0.01 to 5 weight percent of the injected hydrocarbon of an oil-soluble surfactant stable at temperatures up to at least 650 F. Such surfactants are listed in US. Patent 3,357,487 patented Dec. 12, 1967, by R. E. Gilchrist et al.

A few oil-soluble surfactants operable in the invention jected in an amount sufiicient to displace the resultant are listed below: hydrocarbon vapor from the burned out zone and dis- Conc., Trade Name Chemical Name Form Percent Type Dowfax 9N4 Nonylphenol-4 mole ethylene oxide adduct Liquid 100 N onio ic. Igepal DM430 Alkylphenoxypoly(ethyleneoxy)ethanol do 100 Do. Neutronyx 626 Alkylphenolpolyglycol ether containing 6' moles do 100 Do.

ethylene oxide.

Some surfactants operable in the invention which are perse it as condensate deeper in the stratum and, if necessoluble in both water and oil are listed below: sary, to further reduce burned zone temperature to a Conc., Trade Name Chemical Name Form Percent Type Fatchemco Fatty imidazoline l-hydroxyethyl, Z-heptadece- Liquid 100 Cationic.

nyl imidazoline. Deriphat 1700 N-lauryl myristyl beta amino propionic acid .do 50 Amphoteric. Armeen 211T- Secondary fatty amines (di-N-alkyl amincs). Solid" 100 Cationic. Deriphat 151.. Sodium salt of N -coco beta amino propionate .do. 100 Amphoteric. Armeen SZ.-- An alkali metal salt of N-coco amino buturic ac Liquid 40 Do. Triton QS Sodium salt of amphoteric surfactant do 100 Do.

Other surfactants of the various classes may be found safe backfiow level (400 F. or less). Dispersion of hy in Detergents and Emulsifiers (1963 Annual), John W. drocarbon vapor from the burned zone both reduces McCutcheon, Inc., Morristown, NJ. hydrocarbon saturation around the wellbore and has The process is particularly advantageous when applied the advantageous effect of fluidizing more of the oil deeper in thin, heavy oil reservoirs where injected hydrocarbon in the stratum for production during backfiow. The and exhaust gas volumes required for heat transfer are amount of combustion gas to be injected will also vary not prohibitively large, and viscosity reduction benefits With the temperature of hydrocarbon vapor at stratum are the most pronounced. pressure and with the burned zone volume. The minimum A preferred method of igniting the oil stratum around amount to be injected will be the equivalent of one burned the injection production Well comprises injecting a subzone pore volume (measured under stratum conditions stantial slug of an auto-ignitable liquid fuel, preferably of pressure and temperature), but generally suflicient containing an oxidation catalyst, into the stratum through gas is injected so that the amount of heat removed from the well and contacting the slug within the stratum with the burned zone by convection coupled with conductive air or other O -contain'ing, combustion-supportmg gas heat losses during its injection will result in a burned (diluted or enriched air). The use of autoignitable fuels zone temperature of 400 F. or less. in initiating in situ combustion in an oil stratum is dis- In reservoirs in which substantial pressure exists, such closed in the copending application of F. C. Klein and as 500 to 1500 p.s.i., only one burning and backfiow phase M. R. Dean, Ser. No. 559,804 filed June 23, 1966, noW of the operation may be necessary. Under such circum- U.S. Patent No. 3,400,763. Such autoignitable fuels instances the opening up of the reservoir or stratum in the clude tung oil, linseed oil, red oil, castor oil, turpentine, 40 burned-out annulus extending 5 to 30 feet from the well tall oil, tall oil fatty acids, oleic acid, linseed oil fatty provides sul'ficiently increased flow rates of oil from the acids, and mixtures thereof. It is preferred to incorporate natural reservoir pressure to effect good continuous proin the fuel a concentration of oxidation catalyst in the duction from the surrounding stratum. In reservoirs in range of 0.025 to 1.0 weight percent of the fuel. Liquid which the pressure is insufficient to produce oil at a oxidation catalysts are preferred and a representative satisfactory rate, even withthe opening up of the stratum member of this class is cobalt naphthenate. immediately surrounding the well, the in situ combustion The amount of igniter oil to be injected depends upon and backflowing steps are repeated as many times as the the thickness of the stratum ing ignited and is usually operation warrants based upon the oil produced during in the Tange of about 10 to gallons of the ehP the backflow step. By operation in this manner (repeated foot of S ratum h Ckn TO minimiZe the POSSIhIhtY 50 cycles of burning and backflow) around diflferent wells of wellbore fires and to safeguard against high wellbore in a pattern, it is advantageous eventually to drive a temperatures during ignition, it is preferred to follow the di e t-dri mbu tio fr m or o f o o ll to igniter oil with a small slug (on the order of 1 bbl.) of another or to a plurality of wells. To illustrate, when a liquid hydrocarbon (P y diesel fuel) miscible operating in a pattern including a central well and a with the igniter oil and to displace it into the stratum ring of wells, after repetition of the process around each Surrounding the Well y injecting a g of inert gas of the wells a direct combustion drive from either the prior to initiating combustion in the stratum. center well to the ring wells or from the ring Wells to After a combustion zone has been initiated and P P the central well produces most of the remaining oil in gated the desired distance into a stratum by directthe pattern. Similar procedure is effective between parallel air injection, a volume of cool liquid hydrocarbon is 1i f 11 injected Sufficient y to reduce the perature of t It is significant that the cooling steps (hydrocarbon burned Zone to a temperature Close to but Still above and inert gas injection) following the in situ combustion that of the vaporization temperature of Said hydrocarbon has considerable advantage in addition to the lowering at the pressure existing thC stratum. The amount of the temperature of the backflowing fluids In Convenof hydrocarbon to be injected is so minimized in order 35 tional h fi fl fi fl od the b kfl i oil f o to avoid creating an excessive hydrocarbon saturation beyond the Combustion Zone passes through the hot about the wellbore, and will vary both with stratum presburned out area which is at a temperature of above 0 sure and the burned-zone volume and temperature as F. and up to 1100, F. so that Substantial coking of estimated from known reservoir fuel availability and the amount of injected air. For a combustion zone driven 11 decreasin a radical distance in the range of about 10 to 25 feet ductlon and also has the effect of mat la y g from the Well, the amount of hydrocarbon injected is in the permeability of the Stratum through which the comd the ran e of 5 to 50 barrels per foot of stratum thickhustlon Z0116 Passe ness. Fbllowing injection of the hydrocarbon slug, a Thefollowing examples are presented to illustrate t e volume of cool combustion gas may, if desired, be ininvention without unduly limiting the same.

the produced oil takes place. This results in less oil pro- 5 EXAMPLE 1 In applying the huff-puff in situ combustion operation of the invention to an oil reservoir at a depth of about 2400 feet and having a thickness varying from about 12 to 20 feet and an oil gravity of 16 to 18 API, a formation temperature of 111 F., and a reservoir pressure of 750 p.s.i.g., 6.7 barrels (280 gallons) of catalyzed ignitor oil (nine volumes of tung oil to one volume of tall oil fatty acids containing cobalt naphthenate) is injected through a well penetrating the stratum followed by 0.5 barrel (21 gallons) of diesel fuel and displaced into the stratum with combustion gas. Air is injected for 24 hours (150,000 standard cubic feet) and the well is closed in for determining bottom hole temperature to be sure that ignition has been effected. Air is then injected into the ignited stratum to burn out to a 10-foot radius from the well. The air injection rate during the burnout is about 150M s.c.f./d. and a total air required is approximately 700M s.c.f. Preparation for backflow at the end of the burning phase of the operation comprises injecting approximately 60 barrels of diesel fuel followed by injection of flue gas (88% N and 12% S by volume). After a -day period of inert gas injection at a rate of about 150M s.c.f./d., backflow is initiated, the backflowing fluids are produced at a temperature of about 400 F. This operation greatly increases the permeability of the stratum in the -foot radius around the production well.

EXAMPLE 2 Example 1 was repeated in another well except that the five-day inert gas injection of flue gas was omitted. The permeability of the stratum was improved to a marked degree, only slightly inferior to the results of Example 1.

EXAMPLE 3 Example 2 was repeated in another well except that an oil-soluble surfactant, alkylphenoxypoly(ethyleneoxy) ethanol, in the amout of 1 percent of the weight of the diesel fuel was mixed with the disel fuel before injection. The permeability of the stratum was improved to almost that of Example 1 from that of Example 2.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing oil from an oil stratum penetrated by a well and opening up the stratum around the well to improved flow which comprises the steps of:

(a) igniting said stratum adjacent said well;

(b) injecting an O -containing, combustion-supporting gas through said well into the ignited area to drive a combustion zone at a temperature of at least 900 F. radially into said stratum a distance in the range of about 5 to 30 feet at a pressure substantially above normal stratum pressure; (0) thereafter, injecting a substantial slug of liquid hydrocarbon having a carbon chain length of C to C through said well into the hot burned-out zone to substantially reduce the temperature in said zone, form a substantial hydrocarbon vapor slug, and drive a resulting hot zone more remote from said well; and

(d) thereafter, opening said well to production so as to allow stratum pressure to force fluids from said stratum into said well.

2. The process of claim 1 in which between steps (c) and ((1) there is inserted the step (e) of injecting a slug of cool inert gas through said well into said stratum so as to drive said hydrocarbon slug more remote from said well and further cool said zone.

3. The process of claim 2 wherein cooling in steps (0) and (e) is regulated so as to produce fluids in step (d) at a temperature not substantially above 400 F.

4. The process of claim 2 wherein the slug of inert gas is combustion gas.

5. The process of claim 1 in which the hydrocarbon slug contains from 0.01 to 5 weight percent of an oilsoluble surfactant stable at temperatures up to 650 F.

6. The process of claim 1 wherein step (a) comprises injecting a slug of an autoignitable liquid fuel containing an oxidation catalyst into said stratum through said well and contacting said slug within said stratum with an 0 containing combustion-supporting gas.

7. The process of claim 6 wherein said fuel comprises principally tung oil.

8. The process of claim 1 wherein tung oil in an amount in the range of about 10 to 50 gal/ft. of stratum thickness is injected in step (a) and spontaneously ignited with air to ignite said stratum; air is injected in step (b) until said combustion zone is driven a distance from said well in the range of about 10 to 25 feet; and the Slug of hydrocarbon injected in step (c) is in the range of about 5 to 50 barrels/ ft. of stratum thickness.

References Cited UNITED STATES PATENTS 3,171,482 3/1965 Simm 166-261 3,180,412 4/1965 Bednarski et al. 166-260 3,217,800 11/1965 Smith 166-260 3,332,482 7/ 1967 Trantham 166-256 X 3,357,487 12/ 1967 Gilchrist et al. 166-274 X 3,376,929 4/ 1968 Hagedorn 166-261 3,394,759 7/1968 Carey et al. 166-256 3,400,763 9/1968 Klein et al. 166-260 STEPHEN I. NOVOSAD, Primary Examiner US. Cl. X.R. 166-261 

